Small Craft Advisory 1119, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PST WED NOV 21 2012

.SYNOPSIS...ANOTHER BATCH OF SHOWERS WILL MOVE THROUGH WESTERN
WASHINGTON THIS MORNING AND AFTERNOON FOR MORE WET WEATHER. SHOWERS
WILL END THIS EVENING AS HIGH PRESSURE BUILDS OVER THE REGION. A
WARM FRONT WILL BRUSH THE NORTH COAST THURSDAY. A COLD FRONT WILL
MOVE THROUGH WESTERN WASHINGTON FRIDAY. A DRIER WEATHER PATTERN WILL
SET UP OVER THE WEEKEND.

&&

.SHORT TERM...ANOTHER BOUT OF MODERATE TO HEAVY RAIN IS EXPECTED
EARLY THIS MORNING AS ANOTHER WET SYSTEM TRACKS NE THROUGH WESTERN
WA. BUT THIS SYSTEM IS MAKING PRETTY GOOD PROGRESS AND WILL LIKELY
EXIT BY DAY BREAK. THE SATELLITE IS LOOKING CELLULAR OFFSHORE AND
MAY SEE A FEW THUNDERSTORMS AS THE UPPER LEVEL TROUGH SHIFTS INLAND
LATE THIS MORNING AND AFTERNOON. A WINTER WEATHER ADVISORY REMAINS
IN EFFECT FOR THE MOUNTAINS TODAY WITH 3 TO 11 INCHES OF NEW SNOW
EXPECTED. SNOW LEVELS ARE AROUND 3000 FT WITH SNOW POSSIBLE AT ALL
HIGHWAY PASSES. SHOWERS WILL DECREASE THIS EVENING.

A WARM FRONT MAY CLIP THE COAST FOR A LITTLE LIGHT RAIN
TOMORROW...OTHERWISE THANKSGIVING DAY IS LOOKING MAINLY DRY FOR
WESTERN WASHINGTON. THE COAST AND NORTH INTERIOR WILL SEE BREEZY TO
WINDY CONDITIONS AS A FRONTAL SYSTEM STALLS OVER SOUTHERN B.C. THE
BAROCLINIC BAND WILL SHIFT S/SE INTO WESTERN WA LATE THU NIGHT AND
FRIDAY FOR PERIODS OF RAIN. THE MOUNTAINS WILL SEE ANOTHER 1-2
INCHES OF PRECIP WITH MORE HEAVY SNOW ABOVE 4000-5000 FT  IN THE
NORTH CASCADES. THE SNOW LEVEL IS A BIT HIGHER FOR THE CENTRAL
CASCADES AT 5000-6000 FT. BUT EASTERLY FLOW IN THE PASSES WILL
LIKELY KEEP TEMPS NEAR FREEZING...MAKING THE COMMUTE OVER THE
CASCADES A BIT DICEY. WILL PROBABLY NEED SOME WINTER WEATHER
HIGHLIGHTS DURING THIS PERIOD.

MOIST WESTERLY FLOW WILL MAINTAIN A THREAT OF SHOWERS ACROSS WESTERN
WA THROUGH THE WEEKEND. SHOWER COVERAGE LOOKS ISOLATED TO SCATTERED.
FORECAST TEMPS ARE A FEW DEGREES COOLER THAN NORMAL. 33

.LONG TERM...AN UPPER LEVEL RIDGE WILL BUILD INLAND EARLY NEXT WEEK
FOR A PERIOD OF DRY WEATHER. BUT IT IS UNCLEAR HOW LONG THIS PATTERN
WILL LAST AS THE MODELS DIVERGE FROM TUES ONWARD. TOUGH TO PROVIDE
ANY DETAILS AT THIS POINT. THUS LITTLE CHANGES WERE MADE TO THE FAR
EXTENDED FORECAST. 33

&&

.HYDROLOGY...FLOOD WARNINGS REMAIN IN EFFECT FOR THE CHEHALIS RIVER
AT GRAND MOUND AND PORTER...AND FOR THE SKOKOMISH RIVER.

THE CHEHALIS RIVER CRESTED AT GRAND MOUND AND WILL LIKELY FALL BELOW
FLOOD STAGE THIS AFTERNOON OR EVENING. THE RIVER HAS YET TO CREST
AT PORTER BUT IS AWFULLY CLOSE...LESS THAN 1 INCH SHY OF FLOOD
STAGE. BUT BASED ON THE HYDROGRAPH THE CHEHALIS WILL REMAIN NEAR
FLOOD STAGE AT PORTER THROUGH THURSDAY MORNING. THE SKOKOMISH RIVER
IS SLOWLY RECEDING AND WILL FALL BELOW FLOOD STAGE THIS AFTERNOON OR
EVENING.

THE NEXT FRONT WILL MOVE ACROSS THE AREA THURSDAY NIGHT AND FRIDAY.
MAY ANOTHER 1-2 INCHES OF PRECIP IN THE MOUNTAINS BUT LIKELY NOT
ENOUGH TO DRIVE ANY RIVERS INTO FLOOD STAGE. BUT AS ALWAYS WILL NEED
TO WATCH THE SKOKOMISH RIVER. OTHERWISE FLOODING IS NOT EXPECTED
THROUGH THE LONG RANGE FORECAST. 33

&&

.AVIATION...AN UPPER TROUGH AXIS NEAR THE COAST THIS MORNING WILL
MOVE TO ERN WA THIS AFTN...AND A SFC LOW PRES CENTER WILL MOVE FROM
THE SOUTH SOUND REGION TO SOUTH-CENTRAL B.C. THIS AFTN. LOW-LEVEL
ONSHORE FLOW TODAY...LEADING AT TIMES TO A PUGET SOUND CONVERGENCE
ZONE NEAR KPAE AND KAWO. A FLAT UPPER RIDGE WILL MOVE ACROSS WRN WA
LATE TONIGHT. THE AIR MASS WILL REMAIN MOIST AND UNSTABLE TODAY...
THEN BECOME STABLE AND LESS MOIST TONIGHT.

KSEA...A MOIST AND UNSTABLE AIR MASS - IN ADDITION TO AN UPPER
TROUGH AXIS APPROACHING THE TERMINAL THIS MORNING - WILL LEAD TO
OFF-AND-ON SHOWER ACTIVITY THIS MORNING. LOOKING FOR A SURGE OF SW
WIND THIS MORNING AFTER A SFC LOW MOVES NE OF KSEA...GUSTING AS HIGH
AS 30 KT IN THE 15Z-18Z TIME FRAME. SHOWER ACTIVITY WILL CONTINUE TO
A LESSER DEGREE THIS AFTN...THEN END DURING THE EVNG. THOUGH IT IS
UNLIKELY...CANNOT RULE OUT A CLAP OF THUNDER NEAR THE TERMINAL THIS
MRNG. PUGET SOUND CONVERGENCE ZONE WILL REMAIN COMFORTABLY NORTH OF
THE TERMINAL AND APPROACHES TODAY. AS WITH ANY CONVECTIVE SHOWERY
PATTERN...CIGS WILL BE VARIABLE... GENERALLY MVFR CONDS IN -SHRA AND
VFR OUTSIDE -SHRA.    HANER

&&

.MARINE...A 999 MB LOW WAS LOCATED OVER THE SOUTH SOUND EARLY THIS
MORNING. IT WILL REACH THE NORTH CASCADES AROUND 7 AM AND
SOUTH-CENTRAL B.C. BY 10 AM. AS THE LOW MOVE EAST-NORTHEAST...EXPECT
A SURGE OF SW WIND THROUGH PUGET SOUND...AND AN INCREASE IN WEST
WINDS OVER THE COASTAL WATERS AND DOWN THE STRAIT.

WEAK HIGH PRESSURE RIDGING WILL MOVE ACROSS THE WATERS ON WED NIGHT
FOR A MORE TRANQUIL PERIOD. ON THANKSGIVING DAY...A POWERFUL 960-965
MB LOW WILL MOVE INTO THE SE GULF OF ALASKA. THIS WILL INCREASE SE
GRADIENTS AND BRING GALE-FORCE SOUTHEASTERLIES TO THE COASTAL
WATERS...THE WEST ENTRANCE...AND POSSIBLY THE EAST ENTRANCE FROM THU
AFTN THROUGH FRI MORNING. A TRAILING COLD FRONT WILL SLIP SOUTH
THROUGH THE WATERS ON FRI. HIGH PRES WILL BUILD IN BEHIND THE FRONT
FOR A TRANQUIL WEEKEND.     HANER

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WARNINGS REMAIN IN EFFECT FOR PARTS OF THE CWA.

     WINTER WEATHER ADVISORY CASCADES AND OLYMPICS.

PZ...SMALL CRAFT ADVISORY ALL WATERS...FOR HAZARDOUS SEAS AT THE
     WEST ENTRANCE.

     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR CONDITIONS.

&&

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